I have a slow-filling cistern and, having disassembled all the pipes inside I've identified a ripped seal. Assuming that I didn't cause that myself just a moment ago, I'm hopeful that replacing it will solve the problem.
Can you identify it?
It's a Torbeck Cistern Ball Valve Diaphragm Washer
FYI, I used google image search. I cropped the image and searched by image. I don't have an encyclopedic memory of seals.